Perhaps the astrophotographers can help me. The following object was seen at 195 degrees S, from Boston, Massachusetts at 11:50pm or so. It was pretty far above the horizon (maybe 40 degrees?) by the time I photographed it.

I took two full spectrum photos with different lenses. (WB was whatever I last had it set up for, so basically arbitrary.) Camera was Sony APS-C sensor (23.5mm horizontal size, 6000 pixels across).

Sony E 55-210mm, taken at 210mm, F/6.3 0.008" ISO200
Object width around 43 pixels diameter - these images have not been resized, just cropped.

If it was to the right of the moon, I can think of no other answer than Mars, because that is where Mars has been. It is posdible that you are not resolving the disk cleanly for some reason; blurring could certainly make an object appear larger.

Thanks, guys. It does appear to be Mars. I also checked an astronomy app on my phone which confirmed it. However, I still don't know if I can trust that surface detail. The app showed Mars looking vaguely like the above, but it may be confirmation bias on my part.

Here is a visible spectrum capture of Mars from August 2 at 420mm on the a D7100 (24 Mpix), cropped and up-res'ed 2x. Posistion was in the south-west, lots of chromatic aberrations from the atmosphere due to the position close to the horizon. It was very bright, 1/10 sec exposure at f/7.1, -1.3 stops compensation in post. I did also spot what I think was Saturn at the same time a bit further to the west, but did not make any captures of it. I am surprised by the details in your full spectrum capture, especially since it likely was out of focus, making it bigger. I found that focusing on Mars was tricky, finally found a small star in the bright night as focus target.

Yeah, the "details" are either optical artifacts or maybe I got lucky and said artifacts provided additional magnification? Yours looks more like what I was expecting. It really should have been only 6 pixels or so, by the above arithmetic, so I would love to know what is going on.

The lens could almost always auto-focus on Mars. Some failures due to the teleconverter. That's normal. Auto-focus was impossible when the atmospheric conditions were "wavy". But when the seeing was good, the lens did well at AF.

Without the teleconverter, the lens is sharper of course. Look at this next photo where the largest pinpoint of light is Jupiter. There are 3 close moons and two dots far away on the left. I thought those were two moons on the left, but now I do not think so. I don't know whether that faint dot inbetween is a star or a moon. These kinds of photos aren't so great, but I make them just to mark that "I saw this on that night". I get a thrill seeing moons of Jupiter!!
The crop here was rotated to be horizontal. The "axis" in the sky between the left-hand moons dots and Jupiter was more like 45°. I've been meaning to look up what moons were visible that night to confirm this, but have not yet gotten around to it.

Please click this up to the full 1200 px width to see the faint dot in the middle. Resize and conversion to JPG did some harm.

Map of moons for 05 July 2018 at 01:22 UT. I only captured 3 or the 4 Galilean moons.

So if I repeat the above calculations with your camera/lens+teleconverter specs, I get 20 pixels for mars (using 24.25 arcsec -- it varies over time) which is pretty close to your measured 15 pixels. I am definitely concluding that mine was way out of focus.